Question

A cricket ball is dropped from the height of 20 m. (a) Calculate the speed of the ball with which it hits the ground? (b) Calculate the time it takes to fall through this height? [g=10m/s^2]

Answer 1

Answer :

➥ (a) Final velocity (v) = 20 m/s

➥ (b) Time taken (t) = 2 sec

Given :

➤ Intial velocity (u) = 0 m/s

➤ Acceleration due to gravity = 10 m/s²

To Find :

➤ Final velocity (v) = ?

➤ Time taken (t) = ?

Solution :

The speed of the ball with which it hits the ground

From third equation of motion

$\tt{: \implies {v}^{2} = {u}^{2} + 2as }$

$\tt{: \implies {v}^{2} = 0 \times 0 + 2 \times 10 \times 10}$

$\tt{: \implies {v}^{2} = 2 \times 10 \times 20}$

$\tt{: \implies {v}^{2} = 20 \times 20}$

$\tt{: \implies {v}^{2} = 400}$

$\tt{: \implies v = \sqrt{400} }$

$\tt{: \implies \green{ \overline{ \underline{ \boxed{ \purple{ \bf{ \: \: v= 20 \: m/s \: \: }}}}}}}$

Hence, the speed of the ball with which it hits the ground is 20 m/s.

Now ,

The time it takes to fall through this height

From first equation of motion

$\tt{: \implies v = u + at}$

$\tt{: \implies 20 = 0 + 10 \times t}$

$\tt{: \implies 20 = 10t}$

$\tt{: \implies \cancel {\dfrac{20}{10}} = t}$

$\tt{: \implies \green{ \overline{ \underline{ \boxed{ \purple{ \bf{ \: \: t= 2 \:sec \: \: }}}}}}}$

Hence, the time of the ball with which it hits the ground is 2 sec.

⠀

Some releted equations :

⪼ s = ut + ½ at²

⪼ v = u + at

⪼ v² = u² + 2as

Answer 2

Explanation:

hope it will help you ☺️